[llvm] [MC] MCFragment in bump allocator (PR #96402)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-mc

Author: Fangrui Song (MaskRay)

<details>
<summary>Changes</summary>

#<!-- -->95197 and 75006466296ed4b0f845cbbec4bf77c21de43b40 eliminated all raw
`new MCXXXFragment`. We can now place fragments in a bump allocator.


---
Full diff: https://github.com/llvm/llvm-project/pull/96402.diff


3 Files Affected:

- (modified) llvm/include/llvm/MC/MCContext.h (+5-1) 
- (modified) llvm/lib/MC/MCCodeView.cpp (+2-2) 
- (modified) llvm/lib/MC/MCFragment.cpp (+17-19) 


``````````diff
diff --git a/llvm/include/llvm/MC/MCContext.h b/llvm/include/llvm/MC/MCContext.h
index 6c977a5bc0f1f..0f18ce5df1701 100644
--- a/llvm/include/llvm/MC/MCContext.h
+++ b/llvm/include/llvm/MC/MCContext.h
@@ -136,6 +136,9 @@ class MCContext {
   /// objects.
   BumpPtrAllocator Allocator;
 
+  /// For MCFragment instances.
+  BumpPtrAllocator FragmentAllocator;
+
   SpecificBumpPtrAllocator<MCSectionCOFF> COFFAllocator;
   SpecificBumpPtrAllocator<MCSectionDXContainer> DXCAllocator;
   SpecificBumpPtrAllocator<MCSectionELF> ELFAllocator;
@@ -432,7 +435,8 @@ class MCContext {
   MCInst *createMCInst();
 
   template <typename F, typename... Args> F *allocFragment(Args &&...args) {
-    return new F(std::forward<Args>(args)...);
+    return new (FragmentAllocator.Allocate(sizeof(F), alignof(F)))
+        F(std::forward<Args>(args)...);
   }
 
   /// \name Symbol Management
diff --git a/llvm/lib/MC/MCCodeView.cpp b/llvm/lib/MC/MCCodeView.cpp
index 713ae07c3a730..89b28b4da575f 100644
--- a/llvm/lib/MC/MCCodeView.cpp
+++ b/llvm/lib/MC/MCCodeView.cpp
@@ -29,8 +29,8 @@ using namespace llvm::codeview;
 CodeViewContext::~CodeViewContext() {
   // If someone inserted strings into the string table but never actually
   // emitted them somewhere, clean up the fragment.
-  if (!InsertedStrTabFragment)
-    delete StrTabFragment;
+  if (!InsertedStrTabFragment && StrTabFragment)
+    StrTabFragment->destroy();
 }
 
 /// This is a valid number for use with .cv_loc if we've already seen a .cv_file
diff --git a/llvm/lib/MC/MCFragment.cpp b/llvm/lib/MC/MCFragment.cpp
index d90fd34815bda..5347d99e2a4f3 100644
--- a/llvm/lib/MC/MCFragment.cpp
+++ b/llvm/lib/MC/MCFragment.cpp
@@ -203,59 +203,57 @@ MCFragment::MCFragment(FragmentType Kind, bool HasInstructions)
 
 void MCFragment::destroy() {
   // First check if we are the sentinel.
-  if (Kind == FragmentType(~0)) {
-    delete this;
+  if (Kind == FragmentType(~0))
     return;
-  }
 
   switch (Kind) {
     case FT_Align:
-      delete cast<MCAlignFragment>(this);
+      cast<MCAlignFragment>(this)->~MCAlignFragment();
       return;
     case FT_Data:
-      delete cast<MCDataFragment>(this);
+      cast<MCDataFragment>(this)->~MCDataFragment();
       return;
     case FT_CompactEncodedInst:
-      delete cast<MCCompactEncodedInstFragment>(this);
+      cast<MCCompactEncodedInstFragment>(this)->~MCCompactEncodedInstFragment();
       return;
     case FT_Fill:
-      delete cast<MCFillFragment>(this);
+      cast<MCFillFragment>(this)->~MCFillFragment();
       return;
     case FT_Nops:
-      delete cast<MCNopsFragment>(this);
+      cast<MCNopsFragment>(this)->~MCNopsFragment();
       return;
     case FT_Relaxable:
-      delete cast<MCRelaxableFragment>(this);
+      cast<MCRelaxableFragment>(this)->~MCRelaxableFragment();
       return;
     case FT_Org:
-      delete cast<MCOrgFragment>(this);
+      cast<MCOrgFragment>(this)->~MCOrgFragment();
       return;
     case FT_Dwarf:
-      delete cast<MCDwarfLineAddrFragment>(this);
+      cast<MCDwarfLineAddrFragment>(this)->~MCDwarfLineAddrFragment();
       return;
     case FT_DwarfFrame:
-      delete cast<MCDwarfCallFrameFragment>(this);
+      cast<MCDwarfCallFrameFragment>(this)->~MCDwarfCallFrameFragment();
       return;
     case FT_LEB:
-      delete cast<MCLEBFragment>(this);
+      cast<MCLEBFragment>(this)->~MCLEBFragment();
       return;
     case FT_BoundaryAlign:
-      delete cast<MCBoundaryAlignFragment>(this);
+      cast<MCBoundaryAlignFragment>(this)->~MCBoundaryAlignFragment();
       return;
     case FT_SymbolId:
-      delete cast<MCSymbolIdFragment>(this);
+      cast<MCSymbolIdFragment>(this)->~MCSymbolIdFragment();
       return;
     case FT_CVInlineLines:
-      delete cast<MCCVInlineLineTableFragment>(this);
+      cast<MCCVInlineLineTableFragment>(this)->~MCCVInlineLineTableFragment();
       return;
     case FT_CVDefRange:
-      delete cast<MCCVDefRangeFragment>(this);
+      cast<MCCVDefRangeFragment>(this)->~MCCVDefRangeFragment();
       return;
     case FT_PseudoProbe:
-      delete cast<MCPseudoProbeAddrFragment>(this);
+      cast<MCPseudoProbeAddrFragment>(this)->~MCPseudoProbeAddrFragment();
       return;
     case FT_Dummy:
-      delete cast<MCDummyFragment>(this);
+      cast<MCDummyFragment>(this)->~MCDummyFragment();
       return;
   }
 }

``````````

</details>


https://github.com/llvm/llvm-project/pull/96402